Special Note 12/15/07: An individual
with extensive and unique knowledge of Greens Creek geology has
made extensive comments. I am making changes and incorporating
those comments on this page. The first iteration has been
incorporated. More changes will be made.

Introduction

This
is a page on the geology of the Greens Creek Mine. It
includes--or will include when it is complete--references
to and summaries of past work that is public. But
that is not really what this is about. The main thrust of
this page is to present a structural model for the Greens
Creek deposit--one that I think has application to many
other volcanogenic massive sulfide (VMS) deposits in
other parts of the world.

The ideas expressed here have their origin in an
open-ended and free ranging examination of the Greens
Creek deposit undertaken by me in 2004 and 2005. How or
why I was chosen is not clear to me to this day. At the
time I was a web businessman with a background as a
lawyer and a more distant background as a mining
exploration geologist.

The project began with a stint in the core shack
logging core and learning the rocks. From there it went
to reading all of the reports, public and private, on the
property and creating an annotated bibliography. At this
point I tried to incorporate all the recent literature on
geologic basics and this type of deposit, in particular.
Next it involved trying to solve a specific structural
problem. And finally it morphed into a complete
reevaluation of the model of the deposit.

Where
this page is headed . . .
This isn't an official Greens Creek page people at the
mine occasionally look at at it. With that in mind, I
will try to make it as useful as I can for their purpose.
I have also had some comments from folks with a more
scientific-academic bent. Some of that has been critical
and I am now (12/15/07) in the process of making sure
that the page is consistent with their objections to the
extent that I recognize their validity, or that their
point of view is at least discussed. While this page
expresses a point of view and proposes a model, that
point of view and model are not beyond question and
discussion--and revision. This page should be able to
advance the discussion.

Here is a table of some features observed at Greens
Creek and a discussion of their past interpretation and a
revised model. I will add pictures as well as entries in
the future. (There is an issue of whether there is a
structural model in use at Greens Creek currently. That
will be addressed in the future.

There was no exploration
goal in the assignment. It truly was free-form. When I
asked how my work was described to management, I was told
I was doing things the regular geologists didn't have
time to do. At the time, I though the idea was inspired.
(I was having fun, anyway.) Eventually someone disagreed
and the project was ended in August of 2005. (This
coincided with a visit of a group of outside academic
"experts," but I am not sure this was the
cause.)

Despite the
company's ending of support, I continued the project on
my own time. They loaned me thin sections to do some
petrographic work.

So why is this
important? The Greens Creek deposit is explainable
as a rather extreme seafloor collapse, a collapse that
has created rocks that appear to be metamorphic in
origin--in fact they are metamorphic, phyllites to be
more precise. But the paragenesis of the deposit
indicates that the "metamorphism" is
penecontemporaneous--that is it was formed at about the
same time as the rocks were deposited. This meshes
with recent but halting advances in the understanding of
pressure solution as a mechanism to create metamorphic
rock textures in diagenetic or near diagenetic
processes. In short, Greens Creek geology is the
best example I have right now to demonstrate pressure
solution metamorphism. A more theoretical page on
the topic can be found here.

What is the significance of this for
mining exploration? In the case of collapse-related
ore deposits, pressure solution metamorphism becomes a
guide to ore. Textures that were once considered
post-ore can be recognized as related to the ore
depositing event to guide exploration. In addition,
textures and features present at Greens Creek can be
related to other deposits to aid in their
understanding. One striking example that has yet to
be fully developed is the relationship of conglomerates
and buckshot pyrite at Greens Creek to similar features
in the Witwatersrand gold deposits--deposits that have
produced about half of the world's total gold.
Features of banded iron formations such as those in
Western Australia, uranium deposits, and stratiform gold
deposits such as the Juneau Gold Belt deposits,
Kennecott's former Ridgeway Mine, and many others are
also explainable with these ideas. And the
implications go well beyond ore deposits.

Much of this remains
to be developed. This page and the others are works
in progress. I add-to, revise and change what is
here as I think about it and come across new
information. I invite comments and even
participation, as you will see at the bottom of this
page.

A Note about
Notes

To the extent
possible, I have included sources for the information
contained on this page. You can find more about these in
an annotated bibliography at the end. I have also
included notes information about the sequence of
development of ideas. Those notes can be found here. Both of these are under construction.

On to the Substance . . .

Greens Creek is a polymetallic
silver-rich volcanogenic massive sulfide deposit (VMS or
VHMS for Volcanic Hosted Massive Sulfide deposit) located
in they Late Triassic Hyd group. The Hyd contains
sedimentary and volcanic rocks and is interpreted as
having been deposited in a back arc basin.

This is a KGCMC-produced area geology
map that was given to me before I did any work at the
mine. If you click on it a more detailed pdf version is
linked. (A. West presentation, 2004)

This is a cross section that was given
to me at the same time as the map. Green is the
stratigraphic footwall phyllite and gray is the
hangingwall mine argillite. By the trace of the contact,
one can get a hint of the apparent complexity of the
geology. (A. West presentation, 2004)

Here are some grade and
reserve numbers from Freitag (2000). I expect that the
total is about twice this now based on a presentation I
heard last year. I have never been privy to grade and
reserve information.

Below are two stratigraphic section cartoons
showing the approximate relationship of the units. The first
thing to note in these sections is the assumption that the Mine
Argillite is stratigraphically higher. As can be seen in the
cross section above, some of the section is overturned, some is
right side up and some is on its side. I am not aware of
definitive direction indicators in the rocks. Perhaps the
assumption is based on the "normal" sequence where VMS
deposits are found at the end of volcanic cycles--that is where
volcanics stop and sediments begin.

This stratigraphic
section shows the lithologic units using the mine's
terminology and abbreviations. MA stands for"Massive
Argillite" and SA for "Salty Argillite."
MFB stands for "Massive Fine grained Base metal
sulfide," WCA for "White CArbonate ore".
There are other ore designations as well. In the
Phyllite, SP is "Sericite Phyllite" and SPc is
"Sericite Chlorite Phyllite." There are other
designations as well. I will provide more information as
this page is fleshed out. (Source, USGS 1) Immobile
element geochemistry shows the footwall rocks to be mafic
volcanics. (Newberry and Brew)

This version of the section shows some
of the structural style and features. As the map and
cross section farther up and the screen clip below
suggest, the deposit structure is apparently quite
complex. The patterns shown on this section attempt to
summarize my observations. Overall, deformation increases
significantly down section with a radical increase just
above the ore horizon. The conglomerate contains clasts
with preexisting foliation and lithology similar to the
underlying phyllite but enclosed in an apparently later
foliated matrix. Serpentine chlorite clasts are found in
some conglomerates. The right-angle fan of foliation and
spaced cleavage pattern drawn in the phyllite is my
attempt at a characterization of this unit's texture. It
is folded as well. (Source USGS 1, Freitag)

Lithologic Descriptions

Lithologies are fairly well described in
Freitag (2000) and in USGS 1. Below are is a table from Freitag
describing the basic lithologic features:

Additional detail on the ore lithologies can be
found in Freitag's Table 5:

Freitag's tables do not do justice to the very
important conglomerate/breccia units that are found at and below
the ore horizon. I will quote at length from USGS 1:

"The footwall sequence at Greens Creek
contains the discontinuous presence of what are variably
described in the drill logs as silicified conglomerates and
breccias. They occur as 0-30 meter thick lenses of dense,
white to gray, silicified quartz-carbonate, and cherty clasts
in a siliceous matrix. The appearance of the clasts suggests
that their protoliths were derived primarily from the
underlying phyllites and less prevalently, from the footwall
carbonates. Clasts are generally 1-10 cm in size and are
either distinctly sub-rounded or sub-angular, suggesting that
there may be at least two types of breccias. Those containing
sub-rounded clasts tend to be polymictic and are likely
conglomeratic breccias that formed as locally derived debris
flows in response to the onset of late Triassic rifting.
The sub-angular breccias that constitute the majority of
these footwall accumulations are monomictic and are specially
associated with the proximal footwall SR lithology. They are
probably tectonic breccias produced by fracturing of the SR's
after ore formation. Some of these are called foliation
breccias by the mine staff, formed from the intersection of
S2 and S3 foliations. A third less common type of breccia has
been observed in a few locations underground. This is a
polymictic breccia in the immediate hangingwall (or is it
phyllite?) that consists of slightly smaller (1-5cm) clasts
of predominately white quartz pebbles and argillite in a
matrix of fine to coarse crystalline, subhedral pyrite. The
best example to date of this type is located in the 720 ore
access ramp of the upper Southwest orebody within about 20-30
meters of the ore haningwall contact. This breccia, here
interpreted as a conglomeratic lens that formed as a debris
flow during deposition of the hangingwall, is
distinctly different in terms of its stratigraphic position,
size and composition of the constituent clasts, and
composition of its matrix.

"These breccias may have significance
both as indicators of of the tectonic environment at Greens
Creek and as a possible stratigraphic marker horizon. * * *
"

S1 (D1) Foliation noted in
conglomerate clasts. Conglomerate is noted as
being mostly derived from the footwall phyllites.
Foliation is attributed to late Paleozoic
regional deformation.

S2, F2 (D2) Foliation and folding
in all rocks. Foliation is mostly parallel to
bedding except near folds identified as F2 folds.
(Freitag (2000) describes the S2 foliation is
"stylolitic" and of pressure solution
origin.) Shearing is observed on S2 planes. This
event is attributed to Cretaceous metamorphism.

Semi-Ductile Shearing (D2.5) A
large shear zone predates later folding.

S3, F3 (D3) More open folds--the
most recognizable in the mine. Spaced cleavage
and crenulation cleavage associated. Attributed
to later Cretaceous metamorphism.

Klaus Shear: Age uncertain, healed
shear may correlate to the D2.5 event.

F4 (D4) Similar to F3 folds with
parallel fold axes, F4 folds refold F3 axial
planes. May be part of progressive metamorphism
from D3.

Again, Freitag (2000) differs somewhat
in her interpretation of the structure. She lists an
additional deformation of early low angle thrusting
between D1 and D2. She does not address D4. But perhaps
most importantly, she attributes the very extensive
ladder veining that is so important in the Mine Argillite
unit--and as a guide to ore--as being diagenetic. A photo
is shown below the questions section. The mine's model
attributes ladder veining to a Cretaceous D2 event, I
believe.

I am looking for public copies of
diagrams of the structural interpretation of the geology.
They are shown in public on a regular basis, but I don't
have copies right now.

So as we close the "standard
model" on structure structure and lithology, we have
lithologies that indicate rather radical tectonic
activity at the time the rocks were deposited--yet we
have a structural model that does not reflect a bit of
this. Can this be right?

Aside
. . .

Is there
an existing model that is used at Greens Creek or is it
just a mapping scheme? Is it proper to use designations
such as D1 and D2?

It has been pointed out to me that
recent internal company reports don't use "D"
designations at least in part because they suggest events
that may not in fact be real. I agree with this change in
use. Ds prejudice the system against consideration of
progressive deformation. That said, Ds have become part
of the public understanding of the deposit structure.
They are used in Freitag's thesis and in the USGS
summary. Not only that, they are a reasonable inference
from the use of designations such as S2, F3, etc.

If "Ds" are out, is there a
"standard model" at all? Or does this page just
tilt at a straw-man model where none exists? Is it
possible that the existing understanding is consistent
with progressive penecontemporaneous deformation? Of
course if a fold is simply measured in a mapping scheme,
it is a fold whether it was formed around the time of
deposition or in a much later metamorphic event. The
mapping is mapping. To what extent does pigeonholing of a
fold into a designation such as S3 imply a model? Does
speculation in reports about Jurassic or Cretaceous
accretionary metamorphic events make a difference to
this? Or is it still just mapping? I am struggling with
this right now and will make further revisions to address
it.

A Second AsideThe
unconformity issue

When one looks closely at the
structure, metamorphism and stratigraphy at Greens Creek,
it become apparent that whether or not there is an
unconformity at the ore horizon is important. For
example, are foliated clasts in the ore horizon
conglomerate subject to a prior regional metamorphic
event? That is, are they Paleozoic? Or are they Triassic
suggesting penecontemporaneous foliation or emplacement
as clastic intrusives? Or is there some other
explanation? While some age dating has implied that the
footwall is Triassic, questions have remained about the
true stratigraphic placement of the samples and the
reliability of the dates. This should be resolved when
Patrick Sack publishes his PhD work on the footwall. My
personal expection is that they will show Triassic dates.

On to some rocks . . .

An underground "Rib" map showing some
of the complexity of the argillite just above the ore. (Freitag)

And another "Rib" map:

A photo--keep this in mind when you are
reading below . . .

This is one complicated mess . . . or is it?

A Contention: the geologic understanding of the Greens Creek Mine is
in a crisis. The current model--to the extent that there is a
model--appears to rely on a large number of deformational events
yet doesn't begin to explain the apparent complexity of the
deposit. (Note 1)

A new model--or a model in the first
instance--is needed and should simplify the understanding of the
deposit, not add more layers of complexity. It should address the
following . . .

Questions
. . .

These are some
questions that I think need to be answered if an
understanding of the geology of Greens Creek is to be
advanced:

Why does the metamorphic event
that affected Greens Creek seem to be centered on
the ore body while the enclosing rocks are less
metamorphosed or even unmetamorphosed? (See
Newberry et al., photo at bottom of this page)

If conglomerate units indicate
tectonic collapse, why isn't this tectonic event
reflected in the structure? Or is it?

Why does the deformation increase
down-section with a big increase at the ore
horizon? (See Newberry, et al)

Right: Photomicrograph of ladder vein
and stylolite. Note author's interpretation that these
veins are diagenetic. That is at odds with other workers.

From Freitag, 2000.

An Hypothesis: The deformation at
Greens Creek is penecontemporaneous--it happened about the same
time the rocks were formed.

As I attempt to elucidate below, if one
recognizes that the deformation--meaning foliation, folding, and
early faulting occurred at about the same time as the rocks were
formed, the structure of the deposit is understandable as a
simple but intense seafloor collapse. There are other factors in
play, but the great bulk of the apparent complication is
attributable to one event. The complex structure is suddenly
simple.

So, now to support this--to answer the
questions . . .

(or present the beginnings of answers--this is a work in
progress . . . )

It May Look Like Soft Sediment
Deformation, but Can That Be True?

A respected
Alaskan geologist commented to me that he had taken a
tour of Greens Creek in the 1980s and had seen "wild
soft sediment folding" in the ore zone. (C. Freeman,
personal communication, 2005) He isn't the only one to
think that the deformation occurred while the sediment
was still soft. Notwithstanding the appearance of the
rocks, the available papers cited here uniformly state
that this is not the case--or at least their conclusions
hold that high P-T barrovian greenschist facies
metamorphism is responsible for the deformation.

The issue of penecontemporaneous deformation in
VMS footwalls is an old one. Many of the geologists that
have worked at Greens Creek are familiar with the debates
on these matters and I am told that the issue may have
been considered. Perhaps that is why Curt Freeman came
away with the impression he did. While there are vague
reports of consideration--and reports that consideration
of penecontemporaneous deformation is appropriate, I am
aware of no mention of it in any report--certainly not in
any public report.

I would like to back up for a bit. In
order to recognize soft sediment deformation, one needs
to understand what it is. It is not simple and it is not
widely taught in the "hard rock" programs that
mining geologists favor. Certainly--or unfortunately--it
is not something that metamorphic geologists spend much
time with. And it is also not something that happens just
at the surface. The diagram and photos to the right show
some aspects of soft sediment deformation--notably the
continuum of conditions under which progressive
deformation of sediments occurs. These come from Maltman
(1994). Some might recognize the rocks as reflecting the
structural and textural styles of Greens Creek.

Here is an interesting historical
vignette from Maltman on interpretation and
misinterpretation of soft sediment deformation.

From Byrne, Figure 8.1, in Maltman ed.

From Byrne, Figure 8.6(a), in Maltman ed.

From Byrne, Figure 8.7(b), in Maltman ed.

From Martenson, Fig 5.42, in Maltman ed.

From Maltman Figure 9.41, in Maltman ed.

For comparison.

What about Foliation . . .

The
intensity of the foliation in the footwall troubles some
geologists with whom I have raised the idea of
penecontemporaneous deformation. Surely such intense
foliation must be caused by high grade metamorphism--or
must it? First of all, the understanding of what causes
foliations is gradually--I would say haltingly--changing.
Now it is widely recognized that bedding plane foliations
elsewhere--the S2 foliation at Greens Creek is a bedding
plane foliation--are likely to be the result of
diagenetic processes rather than isoclinal folding
events. (See Passchier and Trouw 2005). Spaced cleavages
and and crenulated foliation patterns similar to those
found at Greens Creek are noted in rocks that have
essentially no metamorphic recrystallization.
(Borradaile, et al. 1982) Beginning in the late 1970s and
early 1980s this style of deformation began to be
attributed to pressure solution. (See Gray 1979)

The interesting thing about pressure solution as
a cause of metamorphic textures is its independence from
the normal constraints of pressure and temperature.
Instead of P and T as facilitating factors, one is
looking at porosity and permeability as important factors
as well as such things as grain size, mineralogy, and
stress and strain directions. And pressure solution is
recognized as an important process in diagenesis. The
idea of pressure solution metamorphism is developed
further on this page.

So what about the application of this
at Greens Creek? So far, the work done at the deposit
seems to me to have bypassed the implications of large
scale pressure solution metamorphism--including the very
significant loss of volume it implies. (For example,
Freitag describes the microscale deformation as being
attributed to pressure solution, but applies seemingly
constant volume ductile solutions to the larger scale
features. Diagenesis is recognized on the micro-scale,
but apparently ignored as a factor in larger scale
deformation. The S2 bedding plane foliation is attributed
to Cretaceous isoclinal folding, as are the associated
soft sediment-appearing folds in the ore zone. This is a
recipe for geological confusion and that is exactly what
it has produced.

Simple and logical consideration of
paragenesis may be able to confirm this. More work is
needed on this point

When one recognizes that the
foliation formed at about the same time the rocks were
deposited and lithified, the geology of this apparently
impossibly complex deposit becomes understandable and
actually fairly simple. Occam's Razor has application
here to be sure..

Above
are two photomicrographs from Freitag (2000) of
foliations in Greens Creek footwall rocks.

To the left are two photos from
rocks of the Bull Formation in New York. Despite the
foliation and crenulation, these rocks have undergone
little if any metamorphic recrystallization. A portion of
the author's comments relating to this are copied below
the photos. From Borradaile, et al. 1982.

A closer look at the ore . . .

Like any mine, most of the study at Greens
Creek has been concentrated on the ore zone. It is the best
exposed in workings as well. In this section, I will look at some
of the enigmas of the ore zones.

At least some of the ore at Greens Creek is
reputed to be concentrated in fold noses. One conjecture is that
it was moved there during metamorphism. Partly this is based on
the prior conjecture that the folding is metamorphic, thus any
mobilization must be metamorphic. On the other hand, Freitag
reported that most of the textures in the Lower Southwest orebody
were primary textures and described ore recrystallization as
pre-deformation. Clearly there is some thinking that remains to
be done.

Here is an example of a cross section from the
Lower Southwest Orebody:

Below are some photos and diagrams relating to
Greens Creek ore. With each, I have written some explanation to
attempt to elucidate the issue.

As noted elsewhere on
this page, by far the most thorough and useful study of
Greens Creek ore is that done by Katja Frietag in her PhD
dissertation from the Colorado School of mines. Though
she did this work at the mine, it has not received much
attention there. And much of it conflicts in detail with
other work or working assumptions used by mine staff.

First and significantly, Freitag found that the
majority of textures in the Lower Southwest Orebody were
primary depositional textures. That is they were textures
resulting from seafloor sulfide deposition. Freitag's
figure to the left shows some of these features.

Here is an example of
folded sulfide that I collected and a photomicrograph
made from this piece. The rounded spongy looking minerals
in the photomicrograph are framboids. And framboids are
primary depositional features. (This rock is of interest
because the folding resembles what one would expect from
soft sediment deformation. If the rock was
recrystallized--which it is not--then soft sediment
deformation would be a less likely explanation.)

Freitag's study indicates
that primary textures have been reworked. She attributes
this to sedimentary reworking. Here is an example.

But is that the case?

Below, I will examine some examples.

To the right is a sample
of ore from the 200S orebody. The appearance is that
massive sulfides have been injected into cracks in
veined, but not ductilly deformed, massive argillite. It
doesn't look sedimentary and it doesn't look metamorphic
either.

(Recall here that Freitag
determined the ladder veining to be early--of diagenetic
origin.)

Here us a closer photo of
a chip sawn off of the piece above. The sulfides seem to
be eating away at the argillite. They also seem to be
banded.

Here is another larger
scale example from the 5250 Orebody. Again the sulfide
seems to be eating away at the argillite--and it looks as
if it is flowing.

Here is a photo showing a
sulfide band with apparent flame structures at the top (a
soft sediment structure) and a row of dominos in line
with the pencil. It appears that flow in the more fluid
center part caused the dominos and folding in the lower
layer.

To the right is a section
of sawn massive fine grained base metal sulfide ore--MFB
in the mine parlance. Next to it is a polished section
taken from this piece. Of interest here are the pyrite
grains (the bright grains in the photomicrograph). They
are rounded. This was noted by Freitag as well. The small
black patch in the lower left of the sawn sample is
argillite that contains framboids. A halobia fossil was
found in such a xenolith.

Based
on the examples above, the simplest explanation for all
of these textures is redistribution of sulfide mud in a
near subsurface soft sediment environment. Progressive
lithification may help explain some features too.

Typically at Greens
Creek, massive sulfides are strong and competent in core
or large faces while surrounding rock may be folded and
broken. The photo at the right from the Upper Southwest
Orebody shows some of this. The deformation in the
argillite barely penetrates the massive sulfide. An
explanation for this could be that progressive
lithification of the sulfide caused it to no longer react
as a mud. The D3 deformation evident at the top of the
photo is a result of pressure solution. Since the
sulfides are not amenable to pressure solution
deformation, they have escaped the intense deformation of
the surrounding rocks.

While flow of sulfide mud
may seem attractive from what is presented above, it is
by no means accepted. The more accepted explanation is
that metamorphism moved the sulfides during a high P-T
event. While I have expressed above that I think the
logic for this is dubious, we should look at some of the
theory. Under normal conditions, sulfides are among the
most brittle and strongest minerals.

To the right is a graph from Cox, S.F.,
Ethridge, M.A., and Hobbs, B.E., 1981. The experimental
ductile deformation of polycrystalline and single crystal
pyrite. Econ. Geol., 76:2105-2117. It shows the very high
temperatures and pressures required to deform sulfide
minerals. An interesting thing to note is the inclusion
of marble on the graph. Much of the surrounding rock,
including the massive argillite, is in fact a carbonate
rock. Above I have shown a piece of aragonitic textured
carbonate. Clearly these have not been converted to
marble.

So what did Freitag
conclude?

The figure to the left
is a summary of her interpretation of the sequence of
sulfide formation. The essence of it is that almost all
of it occurred prior to deformation--or at least D2 and
D3, the pressure solution-based deformations. This is
completely consistent with the idea of sulfide mud and
soft sediment deformation. They only try sulfide
deformation she observes is the bent galena cleavage
planes. As can be seen in the graph above, Galena is the
most likely to be impacted and the temperatures and
pressures are attainable in sub-seafloor situations.

As an aside here, many of Freitag's
findings were at odds with the "established
models" for Greens Creek, yet she chose not to make
any significant reinterpretation of the deposit
structure. I expect this would have been very difficult
for her considering the stature of the geologists who
developed the models.

So what do I conclude? It seems apparent that
the sulfides have moved. In some cases they moved as muds, in
some they moved by soft sediment deformation of partly lithified
rocks, and in some cases they were brittlly deformed. (There is
evidence of duplexing in the sulfide masses that I have yet to
document here.) In microscopic detail and in macroscopic form,
the ore bodies are consistent with penecontemporaneous
progressive deformation--that is deformation in a sea floor
collapse.

Now to step back to the larger scale .
. .

Above are two
screen captures from a Hecla promotional video on the
property. The brown is the East Ore--the first area mined
on the property. SWB (or Southwest Bench) is
misrepresented on this drawing. This is essentially the
ore completely separated from the rest of the geology.
None-the-less, it gives one an idea about the
complexity--and the continuity--of the ore.

These models are the best I have but they do not
reflect some of the morphology that is apparent when
manipulating the mine's more powerful program.
Apparently, there is a central keel that is almost flat
lying just above the SW Ore and the 200S Ore.

To the right is a cartoon (to be
revised) that shows the post collapse relationship of the
units. To restore the cartoon to the current situation,
one would rotate it 90 degrees in a clockwise direction.
The central keel is the tongue of argillite in the
center. What is not shown on the cartoon are the melange
ores--the Upper Southwest Ore and the 5250 Ore. These
were highly disturbed during lithification. Their
location is in the center of the keel and they are
separated from the argillite-phyllite contact in places.

Discussion . . .

This is a work in
progress, so this section--as are the other sections--is
subject to change. I apologize if some of the
sections above have not caught up to this one.
Above I contended that the geologic understanding of
Greens Creek faces a crisis. These are the points
that lead me to that conclusion:

Because the structure and
metamorphism observed in the immediate mine area
are inconsistent with regional observations,
regional metamorphism is unlikely to be the
cause.

Textures and structures in the
immediate vicinity of the mine are inconsistent
with the dynamic greenschist metamorphism
postulated as the cause of the deformation.

Microscale observations of mine
rocks are inconsistent with macroscale
interpretations--e.g., diagenetic veining and
dissolution in the Mine Argillite are given no
place in interpretations; pressure solution is
recognized on a microscale, but the volume loss
implications of this process are not recognized
on a macroscale.

Tectonic events suggested by
lithologic units--i.e., conglomerates--are not
reflected in the structural
interpretations.

Outcrops are simply unexplainable
under the established model (see the Rib Maps
above).

Evidence that the footwall is
Triassic is ignored because this data conflicts
with the structural model.

Evidence that the ultramafic rocks
on the property are contemporaneous with
deposition is ignored--probably because no mode
for their emplacement can be imagined.

In her PhD
dissertation, Katja Freitag analyzed and
"unfolded" the Southwest Orebody. She found
that carbonate and sulfide deposits were separated--that
is there was a mound of sulfide ore in one location and a
mound of carbonate ore in a nearby location. A diagram is
shown at the right. Her solution to this problem was to
infer two feeders, on depositing sulfide and one
depositing carbonate--probably at different times. Of
course there was no real evidence of these feeders in the
footwall--they were just inferred. There were little
problems like bits of sulfide here and there in the wrong
place, but those were ignored. The model is here:

A much simpler solution to Freitag's
problem would have been to allow for the possibility of
penecontemporaneous deformation. I don't have a diagram
yet, but it is easy to imagine that the sulfide was
simply pushed off of the carbonate shortly after
deposition. This has been noted at other deposits, but is
not considered at Greens Creek.

Above I suggested that the understanding
can be advanced if it is recognized that the structure is
penecontemporaneous. Below, I will approach this
hypothesis with two lines of logic, first, a deductive
approach--what we would expect to see given geologic
first principles: and second, and inductive
approach--what we would conclude based on the detailed
facts of the situation.

What
we would expect to see . . .

Beginning with the notion that
Greens Creek is a VMS deposit, we know that this
sort of deposit occurs at the end of a volcanic
cycle--or at least the end of a sub-cycle.
In most instances, footwall volcanic rocks are
overlain by sediments deposited in a quiescent
environment. (This inference is so strong
at Greens Creek that it is the basis for assuming
the stratigraphic direction.)

Collapse is to be expected at the
end of a volcanic cycle.

Collapse will manifest itself by
gravity slumping at the surface and soft sediment
deformation in unlithified and partly lithified
strata below the surface.

Newly deposited partly lithified
sediments and volcanics would be highly porous
and permeable and would be very amenable to the
effects of diagenetic pressure solution.
Shear stress and compaction stress would enhance
pressure solution.

Dissolution of substantial
quantities of rock by pressure solution would be
expected to further enhance collapse and could
cause folding and early stage faulting (now
healed) in partly lithified rocks.

Diagenetic pressure solution would
result in foliation of phyllosilicate-bearing
rocks, but would not foliate rocks with
substantial proportions of minerals resistant to
pressure solution. E.g., sulfide-rich
layers would not be subject to pressure solution
and would appear relatively undeformed. In
addition, layers that have low porosity or
permeability would escape pressure solution
deformation. Examples of this could be
aragonite layers. Any feature or structure
that is resistant to pressure solution would be
preserved.

Conglomerates and intraformational
breccias may be formed.

Significant movement on and
between beds would be expected. Because
rocks were in the process of induration when they
moved, it may be difficult to discern the
movement.

Folding would be coaxial since
deformation would be progressive and related to a
single event. We would expect a fair
divergence of attitudes given the nature of the
event.

Sheath folding would be expected
in soft or partially lithified sediments.

Clastic dikes would be expected.

The collapse movement in
combination with pressure solution could
obliterate the larger textures of feeders, but
might allow preservation of some remnants.

Because of the closeness in time,
parts of the alteration system may be
contemporaneous and overprint the deformation.

There are no doubt
other effects that would be predicted--and I can't deny
that my observations may have affected my list.

What we see .
. .

The deposit is stratiform massive
sulfide at the contact of volcanic rocks and
sedimentary rocks suggesting that it is a VMS
type deposit. Abundant syngenetic
depositional textures--e.g., more than half of
the sulfide textures in the Lower Southwest ore
body--confirm this.

Deformation increases down
section.

In thin section, S2, the principle
foliation, is stylolitic--i.e., caused by
pressure solution. S3 is also stylolitic
and pressure solution related. (Freitag
2000) Pressure solution is a major factor
in deformation of this deposit.

D2, D3, and D4 are approximately
coaxial, suggesting progressive deformation.

Metamorphism in the mine area is
much more intense than surrounding areas
suggesting either different processes or
different effects for this area.

There are others too. I will
try to add them later.

So far, the
penecontemporaneous idea seems to be winning, hands
down. So what about the counter arguments?

The
Evidence Against Penecontemoraneous Deformation

There are several lines
of evidence that have been suggested as refutations of
the ideas discussed here. Primarily, these have to
do with recrystallization--or dynamic
recrystallization--suggesting P-T conditions in the
greenschist metamorphic range. Much of this remains
unresolved at this point. Freitag believed that a
static annealing event may have recrystallized--or partly
recrystallized--the massive sulfides.
Notwithstanding that, she found that most textures were
syngenetic.

There are occasional
grains of actinolite approximately parallel to foliation
in the phyllites. I am not sure of the origin of
these. Several possibilities occur to me. One
might be that they are related to the annealing
event. Another is that they are remnants of
propylitic alteration zones. In general, the fine
grained sericite and chlorite that are prevalent in the
footwall phyllites do not have metamorphic overgrowths
and are amenable to and interpretation of low P-T
formation.

Another objection
relates to deformed quartz. There is some
undulatory extinction and even some chess board texture
in quartz in the conglomerates. At this time, I am
not sure what to make of this. Quartz deformation
theory is controversial--at least so far as I am
concerned. Den Brok and others have suggested that
low temperature deformation is possible. And the
conditions for such deformation may be especially
favorable here where much of the quartz is
calcedonic. In any event, I do not see this
objection--if that is what it is--as overcoming the very
significant body of evidence suggesting
penecontemporaneous deformation.

In essense much of the objection
remains amorphous. The idea will not be considered just
because. Or it is asserted that it has been considered
and rejected--even though there is no indication in the
reports. Or the ideas are consistent with current
understanding so we can move on. All of these are
unsatisfying, of course. In some sense that is how science works. People consider what the want to consider.

Metamorphic geologists, in general, are
fairly ignorant of the nature and extent of soft sediment
deformation and diagenesis. Instead they have
concentrated their studies on high temperature and
pressure phenomena. This is starting to change, but the
change is very slow indeed. Many very serious
misconceptions remain--some have yet to be addressed in
even the most cursory fashion. Greens Creek presents an
opportunity to address fundamental issues of
metamorphism, diagenesis, and soft sediment deformation .
. . and to understand this world class ore body at the
same time.

Explain this . . .

Is this sulfide recrystallized?

I don't think so.
Much of the pyrite is framboids.

Above is Triassic Hyd
Group pillow basalt from the Gambier Bay area of
Admiralty Island. Pillows are also found in the immediate
area of the mine as are other primary depositional
features that have somehow managed to escape metamorphic
obliteration. But then again, metamorphic obliteration
may not have happened. (Source: BLM) (It has been
suggested to me that this locale is so far away from
Greens Creek that it is irrelevant. The fact remains that
regionally the Hyd is not a highly metamorphosed unit.)

Future work--other deposits

As I noted above, I believe that the
observations on this page have importance well beyond Greens
Creek. I hope to develop these themes:

VMS deposits very often show more highly
folded and "metamorphosed" footwalls. This is
likely because of pressure solution and collapse in high
temperature, high shear stress, high permeability, high
porosity environment that is very favorable to extensive
diagenetic changes.

The nature of the phyllitic textures at
VMS deposits is informative of the origin of similar
textures elsewhere. That is, textures that are now seen
as metamorphic elsewhere may in fact by diagenetic.

Epigenetic-appearing
"metamorphosed" features at other ore deposits
may be penecontemporaneous or diagenetic. For example,
the Hemlo district was successfully explored as a
syngenetic occurrence, yet likely misinterpretation of
the kinds of features seen at Greens Creek has caused
more recent workers to reject the syngenetic model, most
likely to the detriment of exploration and development.
The conglomerates (or pseudoconglomerates) at Greens
Creek have some characteristics in common with the
conglomerates at Witwatersrand. An understanding
developed at Greens Creek could have positive
implications in these situations and others.

The textures created by the collapse
should provide basinal indicators that will be powerful
guides to ore. (I hope to develop this soon.)

I have collected some information from massive
sulfide deposits in the Hyd Group--Windy Craggy and Woewodski
Island. I hope to post information on these soon. I am also in
the process of scheduling a trip to the Bathurst Camp to support
and discuss the ideas expressed here.

Conclusion--A False Dichotomy

When I was looking at Greens Creek thin
sections with Rainer Newberry, he loaned me the "Atlas of
Deformational and Metamorphic Rock Fabrics" and suggested I
consider the "metamorphic" explanation for the
structure. (I had considered this some time before--after all,
that's what I was taught when I worked there.) But I took the
book and looked for textures that resembled those at Greens
Creek. I found quite a few that were strikingly similar. I looked
deeper. Some of the Greens Creek-like textures were from rocks
that were not recrystallized--i.e., not metamorphosed at all in
the sense that was being advocated. The references pointed to
pressure solution as the cause of the foliations, spaced
cleavages, and crenulations. I learned that pressure solution
doesn't require recrystallization or even induration. In fact,
because it needs fluids and fluid pathways, it may well do better
in rocks that are less mature.

So the bitter debate about the nature of VMS
footwall deformation--'soft sediment' or 'metamorphism'--may have
been a false dichotomy. Both sides may have been right. But the
crux is that the metamorphism was not what people thought. And,
in a sense, the soft sediment deformation was not what people
thought either. Because of the way pressure solution works, soft
sediment deformation and metamorphism--or formation of the sorts
of metamorphic textures we see at Greens Creek--can occur
simultaneously and produce textures structures and fabrics
characteristic of each simultaneously. When one recognizes this
fact, this complex deposit becomes structurally relatively simple
and the knotty problems that had be be ignored can now be
explained.

Freitag, Katja, 2000, Geology and Structure of
the Lower Southwest Orebody, Greens Creek Mine, Alaska, PhD
Dissertation, Colorado School of Mines. At this writing,
Freitag's thesis is the most comprehensive source of basic
information on the geology of the property. It includes most of
the cross-sections, long sections and plans of the Southwest ore
bodies. The work in interesting in its approach. Frietag assumes
the validity of the standard constant volume, high P-T
metamorphism in her work, but at the same time provides
conflicting evidence in her detailed observations.

Newberry, R.J., Crafford, T.C., Newkirk, S. R.,
Young, L.E., Nelson, S.W. and Duke, N.A., Volcanogenic Massive
Sulfide Deposits of Alaska, in Economic Geology Monograph 9,
Mineral Deposits of Alaska, 1997. This contains a brief summary
of the deposit reflecting some information as it was known on the
date of publication.

M. Satre 2004 presentation. A presentation to
the Anchorage convention of the Alaska Miners Association.

USGS1. The USGS has spent considerable time
preparing a volume by Survey people, mine geologists and
consultants that is expected to be more than 300 pages and be
published in their Professional Paper series. Much of that work
was completed a few years ago and I am told that it may be
published soon. It will include almost all of the geologic data
and interpretation as of about 2002. I look forward to
publication of that "sanctioned" volume should assist
this page to move forward as well. I have obtained the
introductory chapter of this work from UAF. Points from that work
are referenced as USGS1.

A West 2003 Presentation. This is one of many
presentations made by mine staff.

The ideas expressed on this page are not in any
way endorsed by Kennecott Greens Creek Mining Company, its staff,
or its parent companies.

Your Comments Here--email to
twelker@alaska.net:

I have some--hopefully they will be up soon.

Some folks have asked for more petrography. Here is a link to a report on the topic. It is a bit
dated--I hope to fix some things in it soon. Still it might be
worth looking at.

In response to comments, I have added more on
foliations.

One person commented that the crystal structure
of clays and micas could be important in understanding the
deformation. This raises and interesting line of inquiry that
needs to be pursued further. The catalyzing action of
phyllosilicates is probably important in understanding the action
of pressure solution. Boles, et al., recently
described low temperature pressure solution of quartz and
feldspar in contact with muscovite. Dissolution rates began in
the range of 1mm per year in their experiment. This is very high
indeed. The movement over a significant volume of rock over even
a brief time would amount to huge change in the rock. At Greens
Creek, the important phyllosilicate in the area of the ore is
"sericite." Sericite isn't a mineral per se, but
probably we are looking at fine muscovite today. Freitag
described annealing that would have converted clay minerals such
as illite to muscovite in any event.

With regard to the concept of
penecontemporaneous deformation, there are a couple of things
that might be considered in regard to Boles' findings. Was there
muscovite formed in the alteration related to the hydrothermal
event that formed the orebody? And would illite or other clay
minerals have the same catalyzing effect that Boles found for
muscovite?

I noted an interesting example of deformation
related to mineralogy in the portal outcrop at the mine. Here a
zone of very sericitic light colored phyllite cuts across darker
chloritic phyllite at a high angle to the foliation. The light
colored rock is very much more deformed than the dark. ET 3/14/07